Adopt new extension host restart lifecycle

[bpasero]

Synopsis
We allow the extension host to be restarted in certain cases. Today this happens without any support for asking components whether they can support a restart and so issues arise.

#180513 introduces a new IExtensionService.onWillStop event that listeners can veto(boolean | Promise<boolean>), for example:

// sync
extensionService.onWillStop(e => e.veto(true, 'component id'));

// async
extensionService.onWillStop(e => e.veto(Promise.resolve(true), 'component id'));

This allows to:

• veto the restart and thus prevent it
• prolong the restart until work has finished without preventing the restart

In addition the method IExtensionService.stopExtensionHosts() is now a Promise<boolean> and callers must await the result before proceeding. For example:

const stopped = await this.extensionService.stopExtensionHosts();
if (!stopped) {
  return;
}

Related Issues
Some components cannot support EH restart without doing some operation first before the EH goes down, for example:

• Data loss: Custom editors do not properly deal with extension host restarts #122992
• Handle EH restart gracefully to avoid notebook working copy data loss #179224

Adoption

• Notebook component should make sure dirty and untitled notebooks are saved before the EH restarts @rebornix
• Custom editor component should make sure dirty and untitled custom editors are saved @mjbvz
• Workspace trust needs to adopt the new boolean return type of stopExtensionHosts here @lszomoru
• Profiles need to adopt the new boolean return type of stopExtensionHosts here @sandy081

[rebornix]

Notebook component should make sure dirty and untitled notebooks are saved before the EH restarts @rebornix
Custom editor component should make sure dirty and untitled custom editors are saved @mjbvz

@bpasero I'm wondering if this can be done in one level up, for example, implement the saving all logic in FileWorkingCopyManager so we don't have to try to trigger saving from notebook or custom editor component.

[bpasero]

But FileWorkingCopyManager has no knowledge about extensions or the extension host restarting. I do not think it should have a dependency to extensions service or stop it from restarting.